The invention relates generally to brake equipment for rail cars, and more particularly to an improved graduated release proportioning valve for empty-load brake equipment to implement a graduated release of braking effort on individual rail cars depending upon whether the rail cars are loaded or empty.
Conventional proportioning valves for empty-load braking equipment are well known in the art. U.S. Pat. No. 4,080,005, assigned to the assignee of the present application, which is hereby incorporated herein by reference, describes a prior art “Empty-load Fluid Pressure Brake System Including Proportioning Valve” for a rail car. As summarized in that patent, a control valve and the brake operating motor are interconnected by a flow path which includes a proportioning valve which is normally biased open and a changeover valve which selectively renders the proportioning valve effective dependent upon whether the car is empty or loaded. In the car-empty setting, the changeover valve permits auxiliary reservoir pressure to be proportionately reduced by the proportioning valve. A spring biases the proportioning valve open. In the empty setting of the changeover valve, this spring delays proportioning action until the quick service brake cylinder pressure development is complete. Thereafter, the proportioning action commences and continues during the development of pressure in the volume reservoir. It will be seen that the initial brake cylinder pressure development is unaffected by the proportioning valve, and this development is not delayed on the empty cars. The quick service feature is thus preserved.
The changeover valve could be manually set in either of its two positions, but it is preferred to use an automatic valve which normally assumes the load setting but on an empty car moves to empty setting as an incident to the automatic control valve moving to service position. The automatic changeover valve includes a means to sense the interval between sprung and unsprung parts of the car, the interval being smaller on loaded cars than on empty cars.
The proportioning valve described above has been manufactured by Wabtec™ as the “P-1 Proportioning Valve”™, as a primary component of the Wabtec™ “SC-1 Empty/Load Equipment”™ for some 35 years. Throughout that time the P-1™ has been a trouble-free valve that has provided highly reliable service on tens of thousands of freight cars.
However, a disadvantage of this proportioning valve, and other known proportioning valves, is that conventional proportioning valves do operate in a graduated release brake system. Recent advances in rail car brake systems include brake systems and equipment which permit rail cars to be controlled in a graduated release braking mode. Therefore, it would be desirable to provide a proportioning valve, similar to the P-1™ proportioning valve described above, except which can be operated in a graduated release braking mode.